This training program is designed so that the investigator-candidate can develop the necessary skills to become an independent physician- scientist. The program builds on the skills and interests attained in the previous three years of a post-doctoral training position, during which the candidate adapted a novel molecular genetic tool for application in the clinical realm. Specifically, mycobaceriophages, viruses which infect Mycobacterium spp. including M. tuberculosis, were designed to express a reporter gene encoding the firefly light-emitting enzyme luciferase upon infection of a viable mycobacterium. This technology, which can be used to rapidly detect M. tuberculosis as well as determine its drug susceptibilities, is much needed to combat the resurgence of tuberculosis associated with the AIDS epidemic. The current application aims to investigate the genetic mechanisms underlying this technology in order to facilitate rational improvements in the systems's performance, while solidifying the candidates facility in the techniques of molecular genetics. The specific aims are to identify phage and host factors which influence the efficiency of the detection scheme. Specifically, the virus has certain features--its lytic phenotype and its shutdown of host protein synthesis which are unfavorable in its adopted role as a producer of receptor genes, yet are required for its effective propagation as a reagent. Cloning the determinants of these two processes will allow their rational regulation. The mycobacterial receptor for phage is an important parameter for both sensitivity and specificity of phage infection; its expression should correlate with the spectrum and degree of infectability of related mycobacteria, some of which are nonpathogens. Knowledge of receptor regulation will help optimize the conditions for performing phage infections, and perhaps allow selective detection of pathogens. The results of this work will produce a superior diagnostic reagent with an extended range of applications, and will likely provide valuable information in the biology of mycobacteriophage and mycobacteria. At the conclusion of the training period, the candidate investigator will have had extensive exposure to the methods of microbiology and molecular biology, and the experience to establish an independent research program in an academic setting, with a close connection to clinical medicine.